Dipping my toe in the UNIX pool

Greetings all,

Since a lot of the positions I'd like to advance to at work make use of unix in one form or another, it's something that I'd like to get familiar with. So I suppose my question is twofold:

I) What's a good book to serve as an introduction to unix?

I guess if it's just to get my feet wet, even a "Dummies..." type book might do. Still, perhaps someone's come across a title that was particularily good and if so I'd like to check it out.

II) Where can I get a copy of unix to install on my system?

I have a PC, and I'd prefer something free, so I suppose that limits my options quite a bit. Something dual-boot friendly with XP would be nice. I'm open to linux or whatever else. Excuse my naivete, but I just want to find a good place to start off and get into the learning process.

Thanks in advance!